Non-metallic enclosures are well known in the electrical industry. These non-metallic enclosures have the advantage of being relatively inexpensive to produce, light weight, and easy to install. In addition, non-metallic enclosures provide an insulating housing for the electrical components contained therein. Typically, non-metallic enclosures are provided with a machined hub extending through the wall of the enclosure for the entry of wiring and other circuitry. The hub further provides a mechanism for coupling the enclosure to a conduit carrying electrical wiring and provides a moisture resistant connection between the conduit and the enclosure. The hub is usually factory installed on the electrical enclosure. The hub generally comprises a male threaded end for threadedly coupling the hub to the enclosure. The enclosure is then installed at the work site and coupled to the conduit.
The conduit in many electrical applications includes a threaded end for coupling the conduit to the electrical enclosure. Accordingly, the hub which has been factory installed in the enclosure includes an internally threaded portion for coupling the conduit to the enclosure. The electrical connection is made by threading the conduit into the hub and the enclosure, followed by feeding electrical wires and circuitry through the hub and conduit. To obtain a weatherproof seal between the conduit and the hub, sufficient torque must be applied to the conduit to tighten the conduit to the hub. In tightening the conduit, torque is transferred directly through the solid hub to the enclosure. This transfer of torque to the enclosure often results in the hub being sheared off the enclosure, resulting in a loose and non-weather tight seal between the hub and the enclosure.
In the past, efforts have been made to prevent or minimize damage to the enclosure caused by over tightening the conduit on the hub. One such method has been to increase the thickness of the enclosure to sufficiently strengthen the wall to withstand the torque being transferred to the enclosure. This method has not been altogether satisfactory and has still resulted in failure of the coupling between the hub and the enclosure. In addition, thickening the enclosure increases the weight of the enclosure and increases manufacturing costs. Other devices which have been produced to prevent failure of the enclosure caused by over tightening the conduit on the hub include the use of a solid hub which is attached to the non-metallic enclosure. The solid hub includes a threaded portion which extends through a hole in the enclosure wall and is secured to the enclosure by a threaded backing ring applied from within the enclosure. The threaded ring is tightened on the threaded portion of the hub against the wall of the enclosure to tighten the hub onto the enclosure and produce a weather-tight seal. The solid hub further includes an internally threaded portion for coupling with a threaded conduit. As the conduit is threaded into the hub and tightened, the hub assembly will rotate before the enclosure is damaged. This type of device, however, has not been entirely satisfactory in preventing damage to the enclosure. In addition, the hub is more difficult to install and secure to the enclosure. The ring may further loosen as the hub rotates when the conduit is screwed into the hub.
Other efforts to minimize damage to the enclosure include the use of a separate union connecting to the hub and to the threaded conduit. The union, however, must also be connected to the hub and can result in damage to the enclosure. In addition, the use of a union increases manufacturing and installation costs.